1. Field of the Invention
The present invention relates to a temperature compensated crystal oscillator and a method of manufacturing the oscillator, and more particularly to a temperature compensated crystal oscillator and a method of manufacturing the oscillator which is intended to achieve compactness of a product by interposing a ring-shaped board having an inner space adapted to accommodate temperature compensating components between a main board and a crystal package.
2. Description of the Prior Art
A crystal oscillator employing a quartz oscillator is an essential component used to generate an oscillation frequency for controlling transmission and reception of signals between mobile communication terminals, and is superior to other oscillators in terms of frequency stability. However, the quartz oscillator has a drawback in that its oscillation frequency varies depending on ambient temperature. To overcome this drawback, the crystal oscillator must be additionally provided with certain components for compensating frequency variation owing to temperature characteristics of the quartz oscillator. Such a crystal oscillator is referred to as a temperature compensated crystal oscillator (TCXO).
In general, a temperature compensating circuit of the TCXO comprises a temperature detection circuit employing resistance variation of a thermistor, a controlled voltage generating circuit for controlling a voltage according to the resistance variation, and a frequency adjusting circuit for adjusting frequency by capacitance regulation according to the controlled voltage. According to presence of the temperature compensating circuit, the TCXO is classified into a one-chip type TCXO using an integrated circuit (IC) chip, and a discrete type TCXO having components such as piezoelectric elements, integrated circuits, capacitors, inductors and resistive elements mounted thereon.
In general, although the discrete type TCXO is superior to the one-chip type TCXO in terms of phase noise characteristic, the discrete type TCXO is difficult to be made compact because it must contain various components. Accordingly, the discrete type TCXO is severely restricted in its adoption into a mobile communication terminal due to its large size despite its excellent characteristics.
FIGS. 1a and 1b are a plan view and a side view showing a conventional discrete type TCXO 100. As shown in FIG. 1a, the discrete type TCXO 100 is configured to have a printed circuit board 101, a crystal package 103 mounted on the printed circuit board 101, and components 105 of a temperature compensating circuit arranged at both sides of the crystal package 103. As appreciated from FIG. 1b, the components 105 are positioned at a level lower than that of the crystal package 103.
The temperature compensating components 105 usually occupy an area 2 to 3 times as large as an area of the TCXO 100 (5.0xc3x973.2 mm2 or 4.7xc3x972.9 mm2). Consequently, the printed circuit board 101 incorporated in the TCXO requires an area far larger than that of the TCXO. Hence, an area of a finished product will also become large (for example, 7.0xc3x975.2 mm2)
As such, there is a considerable limitation to compactness of a conventional temperature compensated crystal oscillator because of a space required to accommodate the temperature compensating components. On this account, such a discrete type TCXO cannot be successfully adopted into mobile communication terminals.
Therefore, there has been strongly required a temperature compensated crystal oscillator and a method of manufacturing the same in the art, in which a space for accommodating temperature compensating components is minimized.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a temperature compensated crystal oscillator which is intended to achieve compactness of a product by a ring-shaped board having an inner space adapted to accommodate temperature compensating components on a main board.
Another object of the present invention is to provide a method of manufacturing the temperature compensated crystal oscillator.
In order to accomplish the above object, the present invention provides a temperature compensated crystal oscillator including a crystal package and at least one component for compensating frequency variation of the crystal package due to temperature variation, the crystal oscillator comprising: a ring-shaped board disposed under the crystal package and comprised of a frame structure having an inner space, the inner space at least as large as a space required to accommodate the temperature compensating component; and a main board disposed under the ring-shaped board and on which the temperature compensating component is mounted within an area corresponding to the inner space of the ring-shaped board.
According to a preferred embodiment of the present invention, the ring-shaped board may have a frame structure coinciding with the crystal package in contour, and the main board may have the same area as that of the crystal package. Therefore, the temperature compensated crystal oscillator can be a finished hexahedral product having the same area as that of the crystal package.
According to another embodiment of the present invention, the ring-shaped board may include at least one conductive pad for connecting the crystal package to a certain circuit on the main board. In particular, when the ring-shaped board has a rectangular structure, the conductive pad is preferably positioned at each of four corners of the ring-shaped board because the crystal package is usually provided at its corners with connecting terminals. Accordingly, if connecting terminals on the crystal package are changed in position, the conductive pad can be correspondingly positioned.
Furthermore, the present invention provides a method of manufacturing a temperature compensated crystal oscillator including a crystal package and at least one component for compensating frequency variation of the crystal package due to temperature variation, the method comprising the steps of: preparing a main board having an upper surface including an area required for mounting of the temperature compensating component; placing the temperature compensating component on the component mounting area of the main board; placing a ring-shaped board on the main board, the ring-shaped board having an inner space at least as large as the component mounting area; and placing the crystal package on the ring-shaped package.